Number + 年
The classifier 年 (nián) is used when counting years or referring to a specific year in time expressions. It appears in phrases like 一年 (one year) and 三年 (three years), and also combines with 中 to form 一年中 (within a year/throughout the year).
我在这个城市已经住了三年了。
wǒ zài zhège chéngshì yǐjīng zhù le sān nián le.
I've already lived in this city for three years.
新的一年又开始了,你有什么计划?
xīn de yì nián yòu kāishǐ le, nǐ yǒu shénme jìhuà?
A new year has begun again; what plans do you have?
她花了两年时间学会了日语。
tā huā le liǎng nián shíjiān xuéhuì le Rìyǔ.
She spent two years learning Japanese.